This invention relates to devices for precisely positioning an object such as a knife blade, tool, or the like. More particularly, the present invention relates to apparatus for converting rotary motion to linear motion with a precise control of the amount of such conversion. The present invention is particularly useful for exact positioning of a tool element such as a knife balde relative to a housing for that blade.
Various prior art devices have been developed for the purpose of accurately positioning a movable object. One technique for producing this result is obtained by employing a relatively large number of cylindrical threads for a small amount of linear travel. One example is the micrometers which typically employ a very fine thread (40 threads per inch generally) between the spindle and sleeve. One complete revolution of the spindle thus advances or retracts the spindle in the sleeve one-fortieth or 0.025 inches. Since greater numbers of threads per inch becomes impractical, measurements of linear increments less than 0.025 inches can only be obtained by counting calibration marks around the circumference of the thimble which is attached to the spindle and also surrounds the sleeve.
Further, a variety of devices have been developed for permitting selectable extension of tool elements such as knife blades relative to an enclosing frame. For instance, U.S. Pat. Nos. 1,406,156 by Cotter et al., 1,755,535 by Bratrud, 1,833,406 by Bratrud and 3,041,724 by Bobkowski all show various arrangements of internal threading configurations for permitting the extension or withdrawal of knife blades from a housing. Various devices have also been suggested for clamping a tool member relative to a retaining housing. One example of such a device using a threaded shaft mounted coaxially in a housing is shown in U.S. Pat. No. 3,486,229 by Fischl. Still further, differential threaded arrangements for accurate linear control of rotary to linear motion conversion have been known. For instance, U.S. Pat. Nos. 2,966,170 by Rawlins and 3,409,271 by Kallenbach show such apparatus for valve stem control.
However, none of these devices provide apparatus for easily and reliably positioning a tool element in a precise location short of utilizing a relatively large number of fine cylindrical threads which become impractical for applications requiring movement of thousandths of an inch. Further, there has been a continuing need for a holding device which is adaptable for retaining any of a variety of tools and extending the position of those tools from a retaining frame in a precise manner and with an easily read calibrated indication of the position.